Tag Archives: wgs84

Convert ESRI Shapefile (.shp) to geoJSON (.json)


Conversion result implemented in Google Maps, using data of my hometown Deinze, Belgium

To convert ESRI shapefiles to geoJSON (which you can perfectly use JavaScript and thus pass on to Google Maps, see screenshot above) you will need GDAL (Geospatial Data Abstraction Library) — Mac Users: download here. I have installed GDAL 1.9 Complete but perhaps the framework itself might also do.

After installation, you can use ogr2ogr to do the actual conversion.

Convert ESRI Shapefile to geoJSON:

/Library/Frameworks/GDAL.framework/Programs/ogr2ogr -f "GeoJSON" output.json input.shp

Convert ESRI Shapefile to geoJSON with Coordinates Conversion (here LAMBERT 1972 (EPSG:31370) to WGS84):

/Library/Frameworks/GDAL.framework/Programs/ogr2ogr -f "GeoJSON" -s_srs "EPSG:31370" -t_srs "WGS84" output.json input.shp

The latter is the command you’ll be looking for when working with gisoost.be buurtwegen data.

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Convert LAMBERT 1972 to WGS84

Needed to convert LAMBERT 1972 (EPSG:31370) coordinates to WGS84 (EPSG:4326) for a project I’m working on in order to use the coordinates with Google Maps (which uses a SphericalMercator (EPSG:900913) projection).

Took me quite a while to find the needed algorithm, so hereby I’m listing them (and am providing the JavaScript implementation):

JavaScript:

var lambert72toWGS84 = function(x, y){

	var newLongitude, newLatitude;

	var n = 0.77164219,
	    F = 1.81329763,
		thetaFudge = 0.00014204,
		e = 0.08199189,
		a = 6378388,
		xDiff = 149910,
		yDiff = 5400150,
		theta0 = 0.07604294;

	var xReal = xDiff - x,
	    yReal = yDiff - y;

	var rho = Math.sqrt(xReal * xReal + yReal * yReal),
	    theta = Math.atan(xReal / -yReal);

	newLongitude = (theta0 + (theta + thetaFudge) / n) * 180 / Math.PI;
	newLatitude = 0;

	for (var i = 0; i < 5 ; ++i) {
		newLatitude = (2 * Math.atan(Math.pow(F * a / rho, 1 / n) * Math.pow((1 + e * Math.sin(newLatitude)) / (1 - e * Math.sin(newLatitude)), e / 2))) - Math.PI / 2;
	}
	newLatitude *= 180 / Math.PI;
	return [newLatitude, newLongitude];

}

Java:

public static Point lambert72toWGS84(double x, double y) {

	double newLongitude;
	double newLatitude;

	double n = 0.77164219;
	double F = 1.81329763;
	double thetaFudge = 0.00014204;
	double e = 0.08199189;
	double a = 6378388;
	double xDiff = 149910;
	double yDiff = 5400150;

	double theta0 = 0.07604294;

	double xReal = xDiff - x;
	double yReal = yDiff - y;

	double rho = Math.sqrt(xReal * xReal + yReal * yReal);
	double theta = Math.atan(xReal / -yReal);

	newLongitude = (theta0 + (theta + thetaFudge) / n) * 180 / Math.PI;
	newLatitude = 0;

	for (int i = 0; i < 5 ; ++i) {
		newLatitude = (2 * Math.atan(Math.pow(F * a / rho, 1 / n) * Math.pow((1 + e * Math.sin(newLatitude)) / (1 - e * Math.sin(newLatitude)), e / 2))) - Math.PI / 2;
	}
	newLatitude *= 180 / Math.PI;
	return new Point(newLatitude, newLongitude);
}

C/C++:

void LambertToLongLat(double x,double y, double& longt, double& lat){
    double n = 0.77164219;
    double F = 1.81329763;
    double thetaFudge = 0.00014204;
    double e= 0.08199189;
    double a= 6378388;
    double xDiff= 150000;
    double yDiff = 5400088.44;
    double theta0 = 0.07604294;

    double xReal = xDiff-x;
    double yReal = yDiff-y;

    double rho = sqrt(xReal*xReal + yReal * yReal);
    double theta = atan(xReal/-yReal);

    longt = (theta0 + (theta+thetaFudge) /n)*180/PI;
    lat =0;
    for(size_t i=0; i<5; ++i){
        lat =(2*atan(pow(F*a/rho,1/n)* pow((1+ e*sin(lat))/(1-e*sin(lat)),e/2)))-PI/2;
    }
    lat *=180/PI;
}

Hope this helps!

Related: if you want to do other transforms (or flip the transorm), check out Transformation between datum’s in JavaScript. Thanks for the tip, Ibrahim (via e-mail)!

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